1. Field of the Invention
This invention relates to an apparatus for making molds for making metal castings, which molds are made from a liquid to pasty composition, which contains in an aqueous phase a binder and, in addition, at least one mineral solid substance, particularly cristobalite, said apparatus comprising two approximately concentrically arranged containers, which are arranged one over the other and adapted to be vacuum-tightly sealed and to be connected to a vacuum pump by lines which are adapted to be shut off, which apparatus also comprises a plurality of pipe lengths, which are arranged in a circular array and interconnect the containers and are adapted to be shut off by respective shut-off valves and serve to transfer the composition from the upper container into the lower container and have inlets, which are open at the bottom of the upper container to a distributing space, which is defined on one side by the cylindrical vertical shell of the upper container and on the other side by a flow guiding surface, and have outlets which are disposed in the lower container over respective cups, which are to be filled.
2. Description of the Prior Art
In a known apparatus of that kind the composition is mixed by means of rotating mixing members in the upper container under a reduced pressure and by said mixing members is also caused to flow or urged into the inlets of the pipe lengths. In the lower container the composition falls from the pipe lengths into the cups to fill the same also under a reduced pressure. The mixer is entirely disposed in the upper container and comprises a drive motor having an output shaft which extends almost as far as to the cover and which carries revolving stirring blades, which extend in a stirring compartment between the housing of the drive motor and the cylindrical shell of the upper vessel. By means of an at least partly perforate, profiled sheet metal element the stirring compartment is separated from a compartment that is disposed in the upper portion of the upper vessel and in which rotatable blades are disposed, which are mounted on the output shaft and can be operated to transfer a pulverulent mixture, e.g., of dry gypsum and cristobalite, from the upper compartment into the water-containing stirring compartment through the perforations of the profiled sheet metal element so that the composition can be formed in the lower compartment. Because the mixing members rotate in the upper container, the known apparatus must be filled to a relatively high degree if an intensive mixing of the composition is to be effected within a tolerable time and a cleaning of the apparatus with a reasonably small loss of material is to be permitted. But a processing of the composition also in small quantities will be required, e.g., in the making of small, high-quality casting molds, particularly if the setting time is shortened by the use of chemical accelerators.
It is also known to provide only one evacuated vessel for a venting of the cups when they are filled under atmospheric pressure. In that case the composition is formed by stirring under atmospheric pressure outside the evacuated vessel. Compared to the operation of the known filling apparatus which has been described first hereinbefore and in which the cups are filled at the same time the processing described in the second place, which is often adopted in small plants, involves a relatively high expenditure of time and labor.